The present invention relates generally to marine structures and specifically to a deep water support assembly for a jack-up type platform structure.
Conventional jack-up type marine structures are commonly used in off-shore oil drilling and production operations in water depths of between 250 to 450 feet. A typical jack-up type structure comprises a platform which serves as a barge for transporting the structure to a work site. Legs are provided at corners of the platform and are movable relative to the platform in a vertical direction.
Construction of a typical jack-up type structure is carried out on dry land. Once the structure is completed, it is floated to a work site and the legs lowered to the marine floor where they are anchored by pilings driven through pile guides in the bases of the legs and into the marine floor. Thereafter, the platform is raised above the marine surface by jacking-up the platform vertically on the legs to a desired height above the marine surface to provide an air gap of 50 to 100 feet. This jacking up of the platform is normally carried out with a jacking mechanism which operates through any known transmission arrangement connecting the legs to the platform. This construction of the typical jack-up structure permits the entire completed structure to be floated to the work site thereby reducing both the cost of building the structure and the time needed to assemble the structure at the work site.
A recent need in the field of off-shore oil drilling for marine structures usable in depths of 500 to 1700 feet of water has not been met by the jack-up type structures described. The expense of constructing a jack-up type structure which would be capable of supporting a platform in such deep waters is prohibitive in the current production market. In addition, technical problems such as providing a sufficiently wide support base which would enable the platform to be adequately supported have been difficult to combine with the jack-up platform concept.
In view of this need for deep water structures and in view of the success of the already existing jack-up technology, it can be understood that there exists a need for a structure that can be employed in deep water but which takes advantage of the time and cost benefits of known jack-up type structures. In addition, since there exists a significant number of already constructed jack-up type structures that are lying idle due to (a) economic conditions and (b) a drop in demand for platforms limited to use in water depths of between 250 and 450 feet, it is desired to find a way to extend the utility of these structures to enable their use in deeper water. This extension of utility could represent a significant savings in the cost of a complete deep water system.